1. Field of the Invention
The present invention relates to a projection apparatus and, more particularly, to a projection liquid crystal projector for enlarging and projecting, on a screen or the like, image information displayed on an optical modulation device such as a color liquid crystal panel.
2. Related Background Art
A variety of conventional color liquid crystal projectors have been proposed as optical modulation devices to display image information on liquid crystal panels and enlarge and project the image information on screens.
FIGS. 9 and 10 show a projection liquid crystal projector described in Japanese Utility Model Publication No. 5-950.
Referring to FIGS. 9 and 10, a case 1 is divided into two chambers through side walls 4 and 5. A light source 9 is arranged in a rear-side chamber 2, and a liquid crystal display drive unit is arranged in a front-side chamber 3. Openings 6 and 7 are formed at the central portions of the side walls 4 and 5. Transparent plates 6a and 7a made of heat-resistant glass are fitted in the openings 6 and 7. A plurality of vent holes 8 are formed in the outer surface of the case between the side walls 4 and 5.
The light source 9 is located at a position opposing the openings 6 and 7 of the side walls 4 and 5 and comprises a lamp 10 and a reflecting mirror 11. The lamp 10 is connected to a power circuit board 12 having a power transformer 13 and a transformer coil 14 through lead wires 15. A polarizing separation prism 16 is arranged in front of the light source 9 to separate light reflected by the reflecting mirror 11 into S- and P-polarized light components. The P-polarized light component passes through the polarizing separation prism 16 and enters a liquid crystal panel 19 of a liquid crystal display drive unit in the front-side chamber 3. The S-polarized light component is guided to the side surface of the polarizing separation prism 16 and emerges from an exit port 17.
Heat dissipation slits 18 are formed in the upper, lower, and side surfaces of the rear-side chamber 2 containing the light source 9. Heat from the lamp 10 is dissipated through the heat dissipation slits 18 and the exit port 17.
A display panel cooler 20 through which the P-polarized light component pass is located at a position opposing the opening 7 in the front-side chamber 3 which accommodates the liquid crystal display drive unit. The P-polarized light component of the beam from the lamp 10 in the light source 9 passes through the display panel cooler 20 and is incident on the liquid crystal panel 19. The liquid crystal panel 19 is connected to a main circuit board 23 through a panel drive circuit board 24 made of a flexible board. A Fresnel lens 21 is spaced apart from the front surface of the liquid crystal panel 19. A projection lens 22 for projecting the beam focused by the Fresnel lens 21 is hold on the front surface side of the case 1 at a position in front of the Fresnel lens 21. Heat dissipation slits 25 are formed in the front and upper surfaces of the front-side chamber 3 incorporating the above components, as in the rear-side chamber 2.
An open space is formed between the liquid crystal panel 19 and the Fresnel lens 21 in the conventional liquid crystal projector described above. The heat dissipation slits 25 formed in the case 1 prevent dust from entering into the apparatus. Since the drive voltage generates static electricity on the surface of the liquid crystal panel 19 driven by the panel drive circuit board 24, the dust is attracted to the surface of the liquid crystal panel 19. As a result, an image enlarged and projected by the projection lens 22 through the Fresnel lens 21 contains an enlarged image of dust, so a high-quality image cannot be obtained.
The heat dissipation slits 18 are also formed in the rear-side chamber 2 for the light source 9 as in the heat dissipation slits 18, and dust enters through the heat dissipation slits 18. The dust attaches to the reflecting mirror 11, the polarizing separation prism 16, and the like to greatly decrease the brightness of the projector.